Field of the Invention
This invention relates generally to the field of geological exploration for hydrocarbons. More specifically, the invention relates to a method of stratigraphic modeling of faults.
Background of the Invention
One of the significant technology hurdles in develop realistic forward stratigraphic models in the environment where there are syndepositional structure movement are the abilities for the model to represent the lateral move of the structure blocks. One typical example is the growth fault, where the previously deposited sediments above the fault (hanging wall) not only moves downwards, but also moves away along the fault from the source of the sediments. Not capturing these lateral displacement of deposits will likely result in unrealistic stacking patterns, erroneous rock property distributions and subsequently significant reduce the applicability of the stratigraphy models and their predictive capabilities.
The starting point for stratigraphic modeling is gridding. Gridding can be described as the process of decomposing a 3D geological volume into a plurality of smaller and simpler 3D volumes, which are typically referred to as cells, finite volumes, control volumes, or finite elements depending on the discretization and simulation techniques being utilized. Accordingly, stratigraphic gridding techniques break a continuous domain into discrete counterparts that can subsequently be used to construct a stratigraphic model by discretizing the equations describing fluid flow, geomechanics, or a combination thereof. In other words, a grid (structured or unstructured) is imposed upon an area of interest in a reservoir or earth model to define a plurality of cells (e.g., non-overlapping polyhedral cells), each having one or more unknown properties associated therewith, that approximate the shape and geometry of the reservoir. The unknown properties serve to characterize the reservoir and can include, but are not limited to, fluid properties such as pressure, temperature or water saturation, and rock properties such as rock lithology, permeability or porosity.
The primary challenge in representing lateral movement of structure blocks in a stratigraphic model is the need for current existing gridding algorithms that can efficiently performs two essential tasks simultaneously: (1) allow the forward stratigraphy model to access the previously deposited sediments in the computational grid efficiently at any location in the computational domain, and at any time during the simulation, for modeling sediment erosion and deposition processes; and (2) allow lateral and vertical movement of any part of the grid to realistically represent the structure move. While a 3D unstructured grid can be re-meshed to represent the structure move realistically, the algorithm is computational expensive and not efficient. More importantly, 3D fully unstructured mesh may not be optimal for forward stratigraphic model, as such a mesh generally needs a significant amount of computations for stratigraphic models to access the sedimentary information stored in the mesh. On the other hand, the structured grid is commonly used in forward stratigraphic model because it provides an efficient way for stratigraphic model to access the sedimentary information stored at any location from the surface. However, the grid does not offer any possibilities for perform lateral translations of any part of the grid without having to resort to a complete re-gridding, which will be computational prohibitive if the operation has to be performed frequently.
Consequently, there is a need for improved methods and systems to enable forward stratigraphic models with faulting.